I will tell you this, when I first got my Betta, I didnt intend to. I wanted to get a guinea pig, but my boyfriend said we just did not have the space for a guinea pig as they also need large homes (most of the cages in pet stores arent big enough for them!) He convinced me to get a fish, as he knew they didn't require GIANT homes like a guinea. I should have done my research, but I didn't. I just got Chops. The pet store said that one- gold fish and bettas can live together, and that they require minimal effort. They tried to talk me into the same 'bowl' my friend has (a little 'decorative' office bowl with no room whatsoever) because it was more expensive. But after I said no to that, they said they only need a bowl. Again, being inexperienced, I got the bowl, gravel, and food they said that they require. After setting everything up, I did my research for several weeks and found out that bowls are NOT GOOD for bettas and even though they aren't giant fish, they need tanks, heat, food, filters, all the works. I have Chops in a 10 gallon, Claudia in a 20, and Felix is in a 2 gallon until I can get a bigger one this weekend.
So, yes, beginners make mistakes, but if someone who knows better tells you what you can do to prolong their lives, then they should listen.
Also, my crowntail I just got definitely has fin rot :/ Nothing I do is fixing it...